Aluminum casting alloy



Patented Sept. 13, 1932 UNITED STATES .PATENT OFFICE No Drawing.

Application filed April 7, 1930. Serial No. 442,467.

' (GRANTED UNDER T1113 AGT OF MARCH 3, 1883, AS AMENDED APRIL 30, 1928 370 G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to the manufacture of aluminum alloy castings, particularly Castings made for internal combustion engines which must be cast from a material having a combination of high strength and ducm tility, both at atmospheric and elevated temperatures, and possessing casting properties which enable it to be cast into intricate design, having a high degree of soundness and good. machinability. My invention is based upon the discovery of an improved aluminum base alloy containing 'copper-nickel-magnesiumiron-silicon and manganese in definite and specific amounts, and a novel method ofincorporating the iron, silicon and magnesium into the alloy in fixed and definite proportions.

There are known alloys possessing similar values of strength and hardness at normal temperatures and others having equally desirable casting properties with same advantage of lightness, but these alloys do not have the combination of properties possessed by the alloy I have invented and am about to describe. The alloy' which is the subject of my invention has advantages over all other knowrrmaterials used in parts requiring high strength, ductility and which must be pressure tight and readily machinable. It has the further advantage of reducing the cost of manufacture owing to its high strength and ductility in the cast condition and susceptibility to heat treatment.

According to this invention the alloying constituents are compounded'in the following proportions in the preferred manner:

Cu 3. 5 per cent Ni 0. 6 per cent Fe 1. 5 per cent Mg 0. 6 per cent S1 0. 6 per cent M11012 0. 5 per cent v Al Difierence alloys that are subject to heat treatment for the purpose of developing desirablephysicial properties is well known and is the basis of i that the presence of other elements has elimtherefore specified 0.6 per cent magnesium purity, and the iron content seldom is less The use of copper in aluminum casting many proprietary, alloys. I have discovered inated the necessity of closely regulating the copper content in the range of 3 to 6 per cent.

However, the effect of copper on the casting properties of this alloy is the same as in the binary alloys of-aluminum and copper and,

in general, the higher the copper content within certain limits, the more desirable the casting properties. Copper, being a heavy metal, increases thespecific gravity of the alloy and therefore I prefer to use as low a copper content as possible within the above range and still obtain perfect castings. This, it will be seen, is somewhat dependent upon the design of the part or casting.

Magnesium forms the intermetallic compound Mg Si with silicon, and in this form has a great hardening and strengthening effect on the alloy I have discovered. I have in the alloy which is the preferred embodio ment of my invention. In ordinary foundry practice it is difficult to control accurately the percentages of the ingredients of an alloy, and'I have therefore allowed a minimum of 0.4 per cent magnesium and a maximum of 0.7 per cent magnesium without greatly a'ffecting the physical properties.

Aluminum ingot of commercial purity contains small percentages of silicon as an imthan 0.5 per cent except in specially prepared high grade material. I have discovered that although theoretically there is suflicient silicon to combine with magnesium to, form the compound magnesium silicide, the silicon present in commercial ingot as an impurity is not all available since it is chemically combined with the iron present in the ingot as an impurity and the iron added to o the alloy as an alloying constituent to form stable compounds or solid solutions of iron and silicon. Therefore, in order to develop the maximum hardening power of the magnesium added to the alloy, I have found it necessary to introduce additional silicon in the form of pure silicon, or in the form of intermetallic alloy, containing silicon, aluminum and other elements as described hereinafter. Ihave discovered that slight exto combine with the iron and magnesium has a pronounced efiect upon the temperature to which castings or parts can be heated during heat treatment. I have also discovered that the presence of primary silicon or silicon in ments as alloying constituents. In the heattreated high strength aluminum alloys, iron is not regarded as a desirable addition. I have discovered that iron, as an added constituent in the alloy, which is the subject of this invention, has a very important function from a commercial stand oint. Where silicon lowers the initial melting point of the alloy, iron increases it. Therefore, parts made from. this alloy can be heated to a much higher temperature during heat treatment and superior physical properties obtained thereby than other alloys of this type without danger of burning. With more than 1.75 per cent iron the casting properties are adversely eii'ected. Therefore, I limit the iron content to not more than 1.75 per cent or less than 0.75 per cent.

Nickel is known to increase the solid solubility of copper in aluminum, both at high and low temperatures. By adding from 0.5 to 1.0 per cent nickel, the precipitation of copper upon aging is prevented. I have found that this amount of nickel lessens the growth or permanent dimension changes in parts cast from this alloy, when subjected to elevated temperatures such as encountered in aircraft engine parts, and increases the elongation in the cast and heat treated conditions.

Manganese is known to improve the tensile strength of aluminum copper alloys cast in parts which are subjected to stress at elevated temperatures, but adversely effects the thermal conductivity. Therefore, I limit the manganese content to 0.2 per cent. I prefer adding manganese to the alloy by means of reduction of manganous chloride in a manner described in my copending application Serial No. 442,468, filed Apr. 7, 1980. The soundness, tensile strength and elongation are thereby greatly improved and the grain structure refined. I prefer to use 0.5 per cent manganous chloride for this purpose altho greater amounts may be used where castings of heavy sections are to be cast.

Having described the amounts and the function of the various alloying constituents, I will now describe the method of incorporating them into the alloy. The aluminum ingot of commercial purity is melted and the copper and nickel are introduced by means of an intermediate alloy or hardener containing approximately 35 per cent copper and 7 per cent nickel. The elements may also be incorporated into the aluminum by adding the copper and nickel separately. Both of these methods are known to the art and I make no claim for any discoveries in this connection; a I

Iron, silicon, and magnesium are introduced into the alloy which is the result of my'invention by means of an intermediate alloy or hardener of definite composition which contains the above elements in proportion to form intermetallic compounds and solid solutions, the composition of which follows:

Per cent Iron 10 Silicon 4 Magnesium 5 Aluminum Difference Having previously prepared the above hardener alloy, I charge the calculated amount to the molten aluminum copper nickel alloy and. soak for at least one-half hour at a temperature of 700800 C. I then add .5% of anhydrous manganous chloride by introducing it beneath the surface of the molten metal by means of an inverted 1IOI1 cup attached to a steering rod or other convenient method and allowed to remain beneath the surface of the molten metal until the reaction is completed. In this manner the manganese chloride is reduced to metallic manganese, the manganese alloying with the aluminum copper nickel, magnesium iron alloy. The metal is allowed to stand for a period of five to ten minutes, skimmed and preferably poured into ingots for the purpose of remelting. For the pouring of sand or chill castings I remelt the alloy, thus made, and just before pouring into the molds I add from 0.5 to 1.5 per cent of nickelous or cuperous chloride, or a combination of the two in the same manner that I added manganese chloride. Standard test specimens cast in this manner in green sand have a tensile strength of 30,000 pounds per square inch and an elongation of five per cent.

The next step in my process is to heattreat the castings or parts by subjecting them to a temperature of 950 to 1000 F. for a period of 1 to 5 hours. The castings or parts are then rapidly coo led either in air. water or other cooling medium. Standard test specimens cast in green sand and treated in this manner have a tensile strength of about 32,000 pounds per square inch and an elongation of eight per cent in twoinches. Where high hardness and strength is required in'the cooling, I reheat to-190 Ci for five hours. In this condition the strength is 50,000 pounds per square inch and Brinell hardness 120.

It is understood that my invention is not limited to the specific details herein described, but can be made in other Ways without departure from the spirit.

I claim: Y

1. The method of producing an aluminum alloy, which consists in forming a composi tion of an intermediate aluminum alloy of 10 parts of iron, 4 parts of silicon, 5 parts of magnesium and 81 parts of aluminum, and then melting together a quantity of said composition metal with aluminum, copper and nickel.

2. A method of producing an aluminum alloy containing aluminum, copper, nickel, iron, silicon and magnesium, which consists in preparing an alloy containing the whole amount of copper and nickel and a predetermined percentage of aluminum; preparing an intermediate alloycontaining predetermined percentages of iron, silicon, magnesium and aluminum, and adding a desired quantity of said intermediate alloy to said first-mentioned alloy.

3. A method of producing an aluminum alloy containing aluminum, copper, nickel, iron, silicon and magnesium, preparing a bimetallic alloy containing the whole amount of copper and nickel, pouring said bimetallic alloy into the melted mass of aluminum, preparing an intermediate alloy of iron, silicon, magnesium and aluminum, then adding a desired quantity of said intermediate alloy.

4. A method of producing an aluminum alloy containing aluminum, copper, nickel, iron, silicon and magnesium, which consists in preparing an alloy containing the whole amount of copper and nickel and a predetermined percentage af aluminum; preparing an intermediate alloy containing predetermined percentages of iron, silicon, magnesium and aluminum, adding a desired quantity of said intermediate alloy to said first-mentioned alloy, and then adding the desired quantity of manganous chloride.

5. A method of producing an aluminum alloy containing aluminum, copper, nickel, iron, silicon and magnesium, which consists in preparing a bimetallic alloy containing the whole amount of copper and nickel, pouring said bimetallic alloy into the melted mass of aluminum; preparing an intermediate alloy containing predetermined percentages of iron, silicon, magnesium and aluminum, addmg a desired quantitv of said intermediate alloy to said first-mentioned alloy, adding the desired quantity of manganous chloride, skimming the slag of? the bath, and then addmg a chloride containing at least one of the metals of the said bimetallic alloy.

6. A method producing an aluminum alloy containing aluminum, copper, nickel, iron,

silicon and magnesium, preparing a bimetallic alloy containing the whole amount of copper and nickel, pouring said bimetallic alloy into the melted mass of aluminum, preparing an intermediate alloy of iron, silicon, 

